Typically, analog to digital (A/D) converters are periodically tested in a system environment to determine if the A/D converter is functioning properly. An A/D converter can be tested by sampling a known voltage and determining if an accurate converted output is provided. The problem previously associated with tests of A/D converters have been related to the accuracy of the known voltage which is used to perform the test. A sampling voltage of the required accuracy is generally difficult to generate. Typical resistor voltage divider circuits do not provide a sampling voltage which is accurate enough. When conventional precision voltage reference circuits are used, substantial circuit size is dedicated for the single purpose of a test voltage function.